Just tell her it's like playing golf with only a driver and a putter....
IMO, I would go with a 3wt and a 7wt. If she caves later on, it leaves a nice opening for a 5wt, but you can get a lot of use on that range. the 7 might be on the high side for trout, but if you get into some larger ones, or want to hit pike, you'll be glad you have it.